Controlling one's blood sugar is the most important aspect in the treatment of diabetes. HbA1c (glycohemoglobin (glycated hemoglobin) A1c) is one example of a blood sugar level indicator. HbA1c is hemoglobin to which the sugar bonds non-enzymatically, and while HbA1c is not affected by short-term changes in blood sugar after meals and the like, the percentage of bonds increases when a high-blood sugar state continues for a long period of time, which causes HbA1c to increase. Hemoglobin has a lifespan of approximately 120 days, and as such, HbA1c is used as an indicator of the blood sugar state one to two months prior to measurement.
Normally, a diabetes outpatient has his/her HbA1c measured once a month when visiting a clinic or the like, and his/her blood sugar state is evaluated by comparing the currently-measured HbA1c with the previous month's measurement value. A course of medication-based treatments is set and dietary/exercise regimens are provided based on the evaluation, and the diabetes patient works to bring his/her HbA1c to a normal value. As such, diabetes patients themselves take considerable interest in changes in their HbA1c.
Thus HbA1c is an extremely important item among indicators of blood sugar states, and is a value of considerable interest to both medical workers and patients alike. However, HbA1c is normally measured at a hospital, using a large measurement device, by collecting the patient's blood. Small-sized devices that measure HbA1c are not widespread, and thus patients cannot know their HbA1c values until they undergo an examination at a hospital.
Furthermore, dedicated small-sized devices for measuring HbA1c are expensive, and require several ul of blood for measurement, which is much higher than the amount required by a blood sugar monitor (1 ul or less). Furthermore, HbA1c by nature changes little from day to day, and thus such a dedicated small-sized device will likely be used comparatively infrequently.
However, even if the device is used infrequently, HbA1c is useful in the self-management of diabetes if it can be measured or checked by the patient him/herself in the same manner as his/her blood sugar level.
In addition to direct measurement using a dedicated measurement device, an estimated value for HbA1c can also be calculated using a plurality of instances of blood sugar level data, as indicated in Patent Literature 1 and 2.
Patent Literature 1 discloses a method in which an average blood sugar level for a given day is calculated from blood sugar level data measured seven times a day, namely before and after breakfast, lunch, and dinner and before going to bed, and an estimated HbA1c value is then calculated based on the average blood sugar level.
Patent Literature 2 discloses a blood sugar monitor having a function for calculating an estimated HbA1c from a plurality of instances of blood sugar level data.
Meanwhile, a blood sugar monitor that outputs an average value of a blood sugar level is known. Patent Literature 3 discloses a blood sugar monitor that divides blood sugar level data found in time series and stored into pre- and post-mealtime groups and outputs an average blood sugar level for each group.
Furthermore, a blood sugar level measurement system that makes it possible to manage the timing of blood sugar level measurements, manage shifts in blood sugar level, and accurately and easily predict future blood sugar levels has been proposed (see Patent Literature 4).
Patent Literature 4 proposes finding individual average values of blood sugar levels at each of seven measurement points, namely before and after breakfast, lunch, and dinner and before going to bed, and furthermore finding a seven-point average value that is the average value of the seven individual average values; the number of times the blood sugar is measured is then reduced based on a correlation coefficient indicating a correlation between the seven-point average value and the respective individual average values.